Continuously manufactured cable

ABSTRACT

Method and apparatus are disclosed for continuously manufacturing a cable of the type having a central conductor around which are concentrically arranged successive outer layers; electrostatic shielding insulation and jacket layers. The method and apparatus includes unique means for vulcanizing the insulation layer and for subsequent cooling.

Unite States Patent Staufler et al.

1 Feb. 29, 1972 QONTINUOUSLY MANUFACTURED CABLE inventors: John Dale Stauffer, Dekalb, lll.; Edwin Henry Arnaudin, Jr., Marion; Willis Lee Chrisman, Fairmount, both of lnd.

Assignee: Anaconda Wire and Cable Company, New

York, NY.

Filed: May 7, 1969 App]. No.: 842,418

U.S. Cl ..425/71, 425/72, 425/113,

425/404 lnt. Cl .1329]! 5/00 Field ofSearch ..18/2 1,4V,6C, IZTT [56] References Cited UNITED STATES PATENTS 2,952,870 9/1960 Mark 18/6 c 3,502,752 3/1970 Brown 1 8/2 3,513,228 5/1970 Miyauchi er al ..18/6 c Primary Examiner-H. A. Kilby, Jr. Attorney-Pennie, Edmonds, Morton, Taylor and Adams 5 7] ABSTRACT Method and apparatus are disclosed for continuously manufacturing a cable of the type having a central conductor around which are concentrically arranged successive outer layers; electrostatic shielding insulation and jacket layers. The method and apparatus includes unique means for vulcanizing the insulation layer and for subsequent cooling.

14 Claims, 7 Drawing Figures FIG.

PATENTEUFEB29|912 3.645.656

SHEEI 1 UF 3 FIG. 6

FIG. 5.

INVENTORS JOHN DALE STAUFFER WILLIS LEE CRISMAN ATTORNEYS EDWIN HENRY ARNAUDIN JR.

PA-IENTEDFEH 29 I912 mm 2 OF 3 INVENTORS JOHN DAL TAUFFER EDWIN HEN WILLIS LEE CRISMAN (a; a, I

ATTORNEYS ARNAUDIN JR.

PATENTEDFEBZS I972 3,645,656

sum 3 OF 3 FIG. 7

CONTINUOUSLY MANUFACTURED CABLE FIELD OF THE INVENTION This invention relates to the manufacture of conductors, and, more particularly, to the manufacture of commercial cables having a central conducting strand of copper surrounded by successive concentric insulating and protective layers.

BACKGROUND OF THE INVENTION It is known to produce cables by taking a central conductor, for example, of stranded copper and extruding thereupon an electrostatic shielding followed by a layer of insulation. The electrostatic shielding is made of a semiconducting material and forms a smooth surface which, if the conductor is used to carry high voltage will obviate corona discharge from the relatively sharply curved outer circumference of the conductor. Another function of the semiconducting electrostatic shield is to provide a smooth conducting surface inside the insulation layer to maintain the inner surface of the insulation at constant potential. These two functions minimize electrical erosion of the insulation layer which is of a polymeric material having high dielectric strength.

As a final step, a jacket of polyvinyl chloride composition may be extruded about the insulated cable, the jacket providing moistureproofing and mechanical protection. Intermediate the jacket and insulation layers it is usual to provide ground wires which maintain the exterior of the insulation layer and inner surface of the jacket at a common potential. As a consequence of the semiconductive shielding and ground wire system, electrical stress across the insulation will be uniform and the possibility of failure of the insulation due to electrical causes is minimized.

The foregoing describes generally the constituents of commercial cable construction. I-Ieretofore, the steps of applying the various concentric layers have been carried out separately, that is to say, discontinuously. Such separate manufacture has required considerable expense, separate storage and handling of the cable at different stages of its manufacture, with the possibility of damage to interior portions of the cable prior to its completion. Furthermore, apparatus which might readily be used during more than one step was unnecessarily duplicated.

It is the object of the present invention to provide an improved method and apparatus for the manufacture of commercial cable by means of a continuous process, which avoids many of the difficulties inherent in prior methods.

It is another object of the present invention to provide a superior method and apparatus for vulcanizing an extruded insulation layer and for cooling the cable thereafter.

SUMMARY OF THE INVENTION In accordance with the teachings of the invention, a method and apparatus are disclosed whereby commercial cable of the type having a central conductor and outer concentric layers thereupon is continuously manufactured by a succession of closely related steps. These steps include the extrusion of a semiconductive shield upon a stranded conductor and immediately thereafter the extrusion of a layer of insulation having high dielectric strength. The insulation is immediately vulcanized by passing through a novel vulcanizing chamber containing a pressurized noncondensing gas and therefrom to a cooling or quenching chamber. Finally, as the insulated cable emerges from cooling it is fed directly into an extrusion head which extrudes simultaneously thereupon a combination of ground wire and outer jacket. In an alternative form of the invention, the jacket is extruded about the insulation layer prior to the vulcanization step. In either case, the continuous process will produce a superior cable and better bonding between insulation and jacket layers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a diagrammatic side view of an apparatus for continuously manufacturing cable according to the invention;

FIG. 2 shows a diagrammatic top view of the apparatus of FIG. 1;

FIG. 3 is an enlarged cross-sectional detail of the fln'mhed cable;

FIGS. 4, 5, and 6 are enlarged sectional views taken respectively along the lines of 4-4 of FIG. 2, 5-5 of FIG. 4 and 6- 6 ofFIG. 2; and

FIG. 7 shows a partial diagrammatic side view of an alternate form of apparatus according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, the apparatus shown comprises the extrusion heads 9 and 10 of which a number of suitable types are known and. which are associated with extrusion machines of a known type (not shown). A cable core 12 continuously enters the extruder 9 where it is covered with a thin layer 1 1 of semiconducting thermoplastic strand shielding that is capable of becoming therrnosetting upon the addition of a suitable vulcanizing agent. A suitable composition for the strand shielding 11 comprises 31 parts of conducting carbon black, such as Vulcan XC-72 available from Godfrey L. Cabot, Inc., 77 Franklin Street, Boston 10, Mass, and 69 parts of ethylene-propylene-(diene monomer) tripolyrner, such as EPDM available from E. I. duPont deNemours & Co., Inc., wherein the diene monomer comprises 1,4 hexadiene. The thickness of the layer 11 is about 5 mils or less and its purpose is essentially to cost the inside surface of the insulation wall with a semiconducting layer that will eliminate areas of electrical stress between the conductor and the insulation wall which might be sources of ionization. The particular advantage of the composition used for the shielding layer 11 is that the composition is itself free from vulcanizing agents and, consequently, temperatures of 430 F. and higher can be maintained at the extrusion die, the reduced viscosity of the extrudate at such high temperature permitting reduction in wall thickness without danger of pinholes.

The core 12 next enters extruder 10 where it is covered with a polymeric insulation layer 13 which is thermoplastic within the extruder head but can be irreversibly cured or set by the application of heat. The combined core 12, shielding layer 11 and insulation layer 13 form a cable 14. A number of suitable polymeric materials having high dielectric strength for forming the insulation layer 13 are known such as natural and synthetic rubbers and polyethylene containing appropriate known types of vulcanizing agents. During the extrusion of insulation layer 13, the vulcanizing agent will diffuse to an extent into the shielding layer 11.

To assist the application of heat to vulcanize layers 11 and 13 core 12 may be heated by resistance or inductive heating means before entering or after leaving extruder head 9 and before entering insulation extruder 10, so that the sensitive heat of the core can contribute to the subsequent curing process.

The extruder I0 extrudes the polymeric covered cable directly into a curing tube or vulcanizing tube 15 which is filled with nitrogen 16 under a superatmospheric pressure supplied by a battery of nitrogen cylinders 17. The pressure in vulcanizing tube 15 is controlled by a reducing valve 18 or other known means to a value such that a compression of cable 14 is effected to prevent the layer 13 from being porous or forming voids or bubbles. It has been found, for example, that a pressure of about 70 to 300 p.s.i. is satisfactory and higher pressures would have disadvantages of requiring the walls of tube 15 be made thicker and require the special construction of end seals. Once the nitrogen 16 has been introduced into tube 15, it remains substantially stagnant or unchanged since there is very little leakage.

The nitrogen 16 serves to transfer heat by convection to the cable 14 in addition to compressing the extruded layers 11 and 13. Since the transfer of heat is essentially radial it is not necessary for the nitrogen to circulate along the tube 15 although, of course, a certain amount of such circulation is unavoidably caused by the advance of the core 12. The

nitrogen 16 is stagnant or unchanged in the sense that'leakage is kept to a minimum by means hereinafter to be explained. This stagnant property of the nitrogen 16 has the important advantage of reducing the heat transfer at the ends of the tube 15 where relatively cool pockets of the gas can accumulate and serve as insulation. Steam-filled tubes cannot function in this manner since steam will condense on any cool surfaces and steam vapor immediately replenishes the condensate.

The tube 15 is seen in FIG. 1 to have the form of a catenary with its highest point at the extruder head and its lowest point at a section 19. The catenary is chosen to match the curvature of the cable 14 as it depends fromextruder 10. Consequently cable 14 and its insulation layer 13 will not touch the walls of the tube 15. A constant curvature is maintained by placing the cable 14 under suitable tension by means of a capstan 21. The core 12 is paid into extruder head 9 and 10 at constant speed by another capstan, not shown. With the cable 14 so maintained in catenary curvature it is a feature of the present invention that the floor 23 of the tube and any continuing tubes or chambers are always separated from the surface of the cable by a gap 24. At the base of the catenary, however, tube extension 26 has a floor 27 which is stepped up from the floor 23 at a distance equal to the gap 24. At this point, however, the insulation 13 will have cooled so that the cable can ride upon the floor 27, which thus serves as the lower terminus of the cable catenary.

The nitrogen gas 16 in the tube 15 is heated by means of hot air and combustion gases from a furnace 28. The heated gases are circulated. through sections 29a, 29b, 29c collectively comprising a jacket surrounding the tube 15. The hot air enters the jacket through a manifold 31 driven by a blower 32 and is returned to the furnace 28 through a manifold 33. A temperature sensing control 35 operating the vent 35a can be adjusted to control the temperature of the recirculation gases which are maintained at about 650 F.

Heavy walls of heat insulation (not shown) cover the out side surfaces of the jackets and manifolds in the usual manner. Very high temperatures, limited only by the heat tolerances of the structural materials of the tube can thus be applied to the apparatus without increasing the internal pressure of the nitrogen 16 which can be released by an appropriate check valve 34 if this is desired. There is an advantage, particularly at high temperatures, to use an inert gas, such as nitrogen, for transferring heat to the polymeric covering 13 since contact with air at high temperature would have an adverse oxidizing effect on the polymer. But it is cheaper to circulate a free gas such as air through the furnace 28 and manifolds 31, 33 which do not then have to be leak proofed beyond the requirements of any hot air system. Nitrogen is also, of course, conserved by the provision, already discussed, that the supply 16 is stagnant.

An important novel feature of our apparatus is comprised in the means for transition between the heated tube 15 and a cooling chamber 36 through which refrigerated water is circulated at high velocity. This transition means is shown most fully in FIG. 4 where the catenary tube 15 is seen to be connected by means of a flange 37 to a flanged cylinder 38 that is welded to an enlarged sump enclosure 39. Similarly a pipe 40 is connected by means of a flange 41 to a flanged cylinder 42 that is welded to the opposite (downstream) end of the enclosure 39.

Projecting inwardly from an upstream wall 43 of the enclosure 39 there is welded a cylinder 44 to which is fastened a retaining plate 46 and projecting inwardly from a downstream wall 47 is welded a cylinder 48 with a retaining plate 49. The retaining plates 46 and '49 combined with the walls 43,47 serve to confine bafile plates 51a, 51b, 51c, and 52a, 52b, 52c and 52d within the respective cylinders 48 and 44. The plates 51a-c and 52a-d are seen to have vertical sides 57,58 (FIG. 5) so that they can be restrained from rotation by guide plates 59a and 59b, and 61a and an opposing guide plate that does not show in the drawing. The cylinder 48, pipe 40, tube section 26 and sump enclosure 39 together comprise the aforementioned cooling chamber 36 through which refrigerated water is circulated.

The water enters the chamber 36' downstream (from the point of view of the cable movement) through a pipe 53 (FIG. 2) and leaves through a pipe 54 that opens into the bottom of the enclosure 39 from a point 56 between the innermost baffle plates 51c. and 52a. The pipe 54 and enclosure 39 constitute a sump for collecting cooling water before it can enter the tube 15. Entry of water into the tube 15 is further prevented by the baffle plates 52a-d which have centered elliptical ad openings 56 sufficiently oversized to assure that the insulation layer 13 will not contact the sides of the openings but small enough substantially to keep water from splashing upstream into the tube 15. It will be understood, in this regard, that the shape of the catenary curve formed by the cable is maintained under close control in a known manner by varying the tension being applied by the capstan 21 in response to a position sensing device within the tube 15. This device is not shown in the drawing but several types are commercially available. The openings 56 a-d are elongated vertically to accommodate the riser of the catenary without permitting contact of the baffle plate with the cable as it advances through our apparatus. The pipe 54 is large enough to provide exhaust gravity flow for all the water from chamber 39 that is needed to cool the largest cable that will be processed in the apparatus.

Pipe 54 empties into a storage tank 62 which is maintained at the system pressure by a connection 63 to the nitrogen line. Storage tank 62 provides a means whereby any nitrogen gas which becomes mixed with water in the sump can separate out into the upper part of the tank and return to chamber 39. The level of water in the storage tank 62 is maintained by a pump 66 having a water source (not shown) whose operation is controlled by known means (not shown) sensing the water level in the tank 62. Water from the tank 62 is circulated at a high speed by another pump 68 through a refrigerator 67 into the tube section 26 just upstream of a conventional series of pressure seals 71 (FIG. 4). The water fills tube section 26 and it is in this section that cooling of the advancing cable is achieved.

Conventional sealscan be used at the downstream end of the tube 26 since the insulation layer 13 is cool and hard as a result of the extraction of heat by the cooling water. A length of pipe 72, however, which contains the seals 71 is dropped so that its floor 73 is lower than the floor 27, thus, the cable which has been riding on the floor 27 can be centered in the seals 71.

Pump 68 is operated continuously to circulate cooling water through tube section, sump or chamber 39 and therefrom to storage tank 62. The bypass pipe 74 and automatic valve 76 are provided to allow excess water to circulate when it is not needed for cooling the chamber 36. Automatic control of the valve 76 and the valve 77 in a pipe 53 connected at its junction 69 with tube section 26 is accomplished as follows: A riser 81 extends vertically from pipe 40 which is immediately downstream of the sump 39. The top of the riser 81 is connected by suitable piping to the top of the tank 62 so that there is high-pressure nitrogen therein above the water level at the pressure of the nitrogen system. A suitable level sensing control 79 is located in the riser 81 for sensing the water/ gas level therein. The control 79 is adapted to activate valves 76, 77 and by this means regulate the flow of coolant into the tube section 26 which will maintain a predetermined height of water in the riser 81. Except for the upstream end of the enclosure 39, the chamber 36 is entirely full of refrigerated, rapidly moving water which enters through the pipe 53 and leaves through the pipe 54. The pressure of the water in tube section 26 and sump enclosure 39 is therefore higher than the pressure of nitrogen by a factor equal to the head of the riser 81. This excess pressure, in combination with the baffle plates 51a-c is sufficient to prevent nitrogen from advancing downstream of the sump enclosure 39. The riser 81 will also accommodate surges of water pressure to an extent which may occur and thus cooperates with the baffle plates 52a-c to prevent the admission of water into the vulcanizing tube 15. It is important to note that prior systems using stream for vulcanizing having a stream cooling water interface actually provided a vulcanizing'tube of indeterminate length because of constant surges of water into the stream filled tube. This defeet is eliminated by the present invention.

Except for slight amounts of nitrogen which have dissolved in the water and thereafter escapes past the seals 71 there is essentially no nitrogen loss, with the result that the body of nitrogen remains stagnant or unchanging and the cost of this gas is negligible except for refilling after shutdown. The nitrogen provides means for maintaining the covering 13 under pressure during curing and cooling and of transferring heat to the covering from the circulating hot air. Transfer of heat from the nitrogen to the cooling water is minimized by the fact that water contact with nitrogen is essentially restricted to the sump enclosure 39 since the water is withdrawn so rapidly by gravity flow from the sump that it cannot enter upstream past the baffle-plates 520-11. The nitrogen in the sump enclosure 39 is rapidly cooled, and since it is stagnant serves as heat insulation against heat transfer from the water to the hotter nitrogen body. The difference between the disclosed arrangement and a steam vulcanizing system of the usual type is of great importance to obtain the maximum cooling effect from the water, for if the nitrogen was replaced by steam, not only would the insulating effect of the cooled nitrogen be lost but the heat of vaporization and sensitive heat of water condensed from the stream would be added to the cooling load. As a result it has been found that the length of the cooling chamber 36 required by our apparatus is one-third less than that required in conventional steam vulcanizers.

However, the sump and baffle-plate combination of the interface of the heating-cooling system will have useful application to systems employing steam either live or superheated, instead of nitrogen. When used in a steam system positive pumping means should be installed in the pipe 54 to withdraw a small amount of steam, along with the water.

After emerging from seals 71, the now insulated cable is first dried by a sponge-type drier (not shown) such as described in US. Pat. No. 3,386,120 and is then fed directly into a jacket extruder 82 to complete the process of manufacturing. The rate of extrusion in the extruder 82 will be governed largely by the rate at which vulcanization and cooling of the cable takes place previously. With reference to FIG. 6, the extruder head 83 is shown depositing in combination, an extruded semiconducting polymeric coating 84 in which are embedded axially arranged ground or drain wires. By this method of manufacture, the drain wires are applied during the extrusion operation at extrusion speeds and the wires are securely embedded in the semiconducting jacket. Upon leaving the head 83, the cable passes through an apparatus 85 which may be solely a cooling apparatus, or if vulcanizing and cooling is required, the apparatus 85 may be similar in all respects to that hereinabove described.

In an alternate form of the present invention (see FIG. 7), the jacket extrusion step is accomplished immediately following extrusion of the insulation layer. Accordingly, there are provided extrusion heads 9, 10' and 83', the latter being directly connected in sealing engagement with the vulcanizing tube Although the extruder heads have been shown separately, it will be understood that a single multiple extruder may be used. Prior to the insulation extrusion step, where separate extruders are employed, the core may be heated by an electric induction means {not shown) to add the sensitive heat of the core to the vulcanizing heat provided in the tube 15'. Tube 15 is similar to tube 15 previously described, and will be connected to a cooling chamber similar to chamber 36.

In either of the two forms of jacket extrusion immediately described above, there are particular advantages achieved by having the jacket step performed as a continuous part of the overall cable manufacturing process. For example, in the primary form described in FIGS. 1-6 wherein the jacket is extruded subsequent to vulcanization and cooling of the insulation layer, the continuous process provides superior joining of the jacket to the insulation. One reason for this is that the insulation is entirely free from contamination, distortion, damage or other defects which might very well occur through handling and storage of the insulated cable prior to a delayed final jacket extrusion step. In a process where the jacket requires vulcanization, the bonding effect between jacket and insulation can be further increased, if desired, by undercuring the insulation and curing it finally during vulcanization of the jacket.

A further advantage not so readily apparent is produced by subjecting the metal core for a prolonged period of time to the high heat of the vulcanizing tube 15. During the course of vulcanization of the insulation layer, the metal core becomes heated to a very high temperature and even after the cable has proceeded through the cooling chamber 36, the core remains at an elevated temperature (for example, about F.) This sensitive, retained heat of the core is useful during the jacket extrusion process which immediately follows and will aid in achieving a good bond between the jacket and insulation layers. It is important that this bond be free from voids which might produce corona discharge effects.

The valuable advantages of superior bonding and protection of the insulation layer from defects just referred to with respect to extruding the jacket subsequent to vulcanization and cooling of the insulation layer also apply where the jacket is extruded about the insulation layer prior to the vulcanization step as illustrated in FIG. 7. Of course, in this case the jacket is of a type which requires vulcanization and naturally, due to the combined thicknesses of the respective layers, vulcanization will proceed more slowly.

It will be understood that the foregoing description has related to a particular embodiment or embodiments of the invention and therefore is merely representative. In order to understand fully the spirit and scope of the invention, attention is directed to the appended claims.

We claim:

1. Apparatus for making coated electric cable comprising a tube forming a vulcanizing chamber, a gas inlet to said chamber connected to a pressure source of gas, an extruder head in sealed relation to and at one end of said chamber for continuously extruding a coating on said cable and for feeding the covered cable into said chamber, means for heating said gas, a cooling chamber located downstream of said vulcanizing chamber, means provided to circulate cooling water through said cooling chamber, a sump intermediate and in fluid flow communication with said vulcanizing and cooling chambers, means for withdrawing cooling water from said sump, first baffle means between said withdrawing means and said vulcanizing chamber, and second baffle means between said withdrawing means and said cooling chamber, said baffle means acting to prevent the admission of water into the vulcanizing chamber and having openings for the free passage of said cable therethrough without contacting said cable.

2. Apparatus according to claim 1 in which the heating means comprises a jacket surrounding said tube, a combustion burner connection to said jacket, means for circulating and recirculating heated air and combustion gases through said jacket and means for sensing the temperature of the recirculated gases to control the heat transmitted from said jacket to the gas in the vulcanizing chamber.

3. Apparatus according to claim 1 in which the tube forms a catenary curve, means are provided to draw the cable through said tube, and the cable depends from the extruder head throughout the length of the tube without contacting the walls thereof.

4. Apparatus according to claim 3 in which a riser is located downstream of said sump, said riser being connected to the gas pressure source and control means sensing the level of water in said riser to regulate the height of water therein and the degree of counteracting pressure exerted by the water in said cooling chamber against gas pressure upstream of the cooling chamber, said riser and battle means cooperating to prevent surges of cooling water from entering the vulcanizing chamber.

5. An apparatus for continuously extruding and curing an advancing polymeric strand comprising an extrusion head for said strand, a tube extending downstream directly from said head, a substantially unchanging body of inert gas filling said tube around said strand, means for maintaining said gas at superatmospheric pressure, a jacket surrounding said tube, means continuously circulating a fluid through said jacket at essentially ambient pressure, and means external to said jacket heating said fluid to a temperature sufficient for rapidly curing said strand, said gas conveying heat by convection from said fluid to said strand, a cooling chamber located downstream of said tube, means provided to circulate cooling water through said cooling chamber, a sump intermediate and in fluid-flow communication with said tube and said cooling chamber, means for withdrawing cooling water from said sump, first baffle means in said sump between said withdrawing means and said tube, and second baffle means in said sump between said withdrawing means and said cooling chamber, said baffle means acting to prevent the admission of water into the tube and having openings for the free passage of said cable therethrough without contacting said cable.

6. Apparatus for vulcanizing polymeric coatings and the like on an electric cable comprising a tube forming a vulcanizing chamber, means for maintaining a noncondensing gas under relatively high pressure conditions in said chamber, jacket means surrounding said chamber, means for circulating a hot fluid at ambient pressure through said jacket to heat said gas, means permitting passage of a cable through said chamber while maintaining said gas in an essentially stagnant condition, a cooling chamber located downstream of said vulcanizing chamber, means provided to circulate cooling water through said cooling chamber, a sump intermediate and in fluid-flow communication with said vulcanizing and said cooling chambers, means for withdrawing cooling water from said sump, first bafile means in said sump between said withdrawing means and said vulcanizing chamber, and second baffle means in said sump between said withdrawing means and said cooling chamber, said baffle means acting to prevent the admission of water into the vulcanizing chamber and having openings for the free passage of said cable therethrough without contacting said cable.

7. An apparatus for continuously curing and cooling an advancing polymeric strand comprising a tube containing a pressurized gas at elevated temperature, means defining a chamber downstream of and communicating with said tube, a sump opening downwardly in said chamber immediately downstream of said tube, refrigerating means, pumping means, piping means connecting said sump to a point in said chamber substantially downstream of said sump through said refrigerating means and said pumping means, said pumping means continuously circulating cooling water from said sump to said downstream point in said chamber, first baffle means in said sump between said piping means and said tube, and second baffle means in said sump between said piping means and said chamber, said baffle means acting to prevent the admission of cooling water into said tube and having openings for the free passage of said strand therethrough without contacting said cable.

8. The apparatus of claim 7 wherein said tube is formed in a catenary comprising means suspending said strand in a catenary within said tube and said chamber without contact between said strand tube and chamber.

9. The apparatus of claim 8 wherein said openings are vertically elongated to accommodate the catenary rise of said strand.

10. The apparatus of claim 11 including a tubular extension projecting substantially horizontally from the lowest point of said catenary, said extension comprising a support for said extrudate suspended in said catenary, the floor of said extension being abruptly elevated above the floor of said catenary tube at said lowest point thereof.

11. Apparatus for continuously manufacturing an electrical cable having a plurality of concentric coatings comprisin first extruder means for receiving and depositing upon an e ectncally conductive core at least one polymeric coating, a vulcanizing tube connected to said extruder means to receive the coated core, means for maintaining a gas under high heat and pressure in said vulcanizing tube, liquid cooling means connected to said vulcanizing tube for receiving the coated core after passing through the vulcanizing tube, sump means intermediate and in fluid flow communication with said vulcanizing tube and said liquid cooling means, means for withdrawing cooling liquid from said sump, first baffle means between said withdrawing means and said vulcanizing tube, second baffle means between said withdrawing means and said liquid cooling means, said baffle means acting to prevent the admission of cooling liquid into said vulcanizing tube and having openings therethrough for the free passage of said cable therethrough without contacting said cable, jacket extruding means for receiving the coated core directly upon leaving the cooling means and for depositing about the core an extruded jacket, and means for cooling the extruded jacket.

12. The apparatus in claim 11 wherein said tube and at least upstream portions of said liquid cooling means are formed in a catenary curve matching the natural depending configuration of the core to prevent contact between the coated core, tube and cooling means until the coating is sufficiently hard, the first-mentioned extruder means comprises means for depositing upon said core a semiconducting shield layer and thereafter an insulation layer, and the jacket extruder deposits drain wire embedded in said jacket.

13. The apparatus according to claim 11 wherein the tube is filled with an inert noncondensing gas, a jacket surrounds the tube and means are provided for recirculation of hot combustion gases throughout said jacket, the tube is in direct communication with the cooling means comprising cooling water thereby forming a gas-water interface and means are provided for circulating water throughout the cooling means without admission of water into the vulcanizing tube.

14. The apparatus of claim 7 wherein means are provided for heating the core prior to entering the extruder means. 

1. Apparatus for making coated electric cable comprising a tube forming a vulcanizing chamber, a gas inlet to said chamber connected to a pressure source of gas, an extruder head in sealed relation to and at one end of said chamber for continuously extruding a coating on said cable and for feeding the covered cable into said chamber, means for heating said gas, a cooling chamber located downstream of said vulcanizing chamber, means provided to circulate cooling water through said cooling chamber, a sump intermediate and in fluid flow communication with said vulcanizing and cooling chambers, means for withdrawing cooling water from said sump, first baffle means between said withdrawing means and said vulcanizing chamber, and second baffle means between said withdrawing means and said cooling chamber, said baffle means acting to prevent the admission of water into the vulcanizing chamber and having openings for the free passage of said cable therethrough without contacting said cable.
 2. Apparatus according to claim 1 in which the heating means comprises a jacket surrounding said tube, a combustion burner connection to said jacket, means for circulating and recirculating heated air and combustion gases through said jacket and means for sensing the temperature of the recirculated gases to control the heat transmitted from said jacket to the gas in the vulcanizing chamber.
 3. Apparatus according to claim 1 in which the tube forms a catenary curve, means are provided to draw the cable through said tube, and the cable depends from the extruder head throughout the length of the tube without contacting the walls thereof.
 4. Apparatus according to claim 3 in which a riser is located downstream of said sump, said riser being connected to the gas pressure source and control means sensing the level of water in said riser to regulate the height of water therein and the degree of counteracting pressure exerted by the water in said cooling chamber against gas pressure upstream of the cooling chamber, said riser and baffle means cooperating to prevent surges of cooling water from entering the vulcanizing chamber.
 5. An apparatus for continuously extruding and curing an advancing polymeric strand comprising an extrusion head for said strand, a tube extending downstream directly from said head, a substantially unchanging body of inert gas filling said tube around said strand, means for maintaining said gas at superatmospheric pressure, a jacket surrounding said tube, means continuously circulating a fluid through said jacket at essentially ambient pressure, and means external to said jacket heating said fluid to a temperature sufficient for rapidly curing said strand, said gas conveying heat by convection from said fluid to said strand, a cooling chamber located downstream of said tube, means provided to circulate cooling water through said cooling chamber, a sump intermediate and in fluid-flow communication with said tube and said cooling chamber, means for withdrawing cooling water from said sump, first baffle means in said sump between said withdrawing means and said tube, and second baffle means in said sump between said withdrawing means and said cooling chamber, said baffle means acting to prevent the admission of water into the tube and having openings for the free passage of said cable therethrough without contacting said cable.
 6. Apparatus for vulcanizing polymeric coatings and the like on an electric cable comprising a tube forming a vulcanizing chamber, means for maintaining a noncondensing gas under relatively high pressure conditions in said chamber, jacket means surrounding said chamber, means for circulating a hot fluid at ambient preSsure through said jacket to heat said gas, means permitting passage of a cable through said chamber while maintaining said gas in an essentially stagnant condition, a cooling chamber located downstream of said vulcanizing chamber, means provided to circulate cooling water through said cooling chamber, a sump intermediate and in fluid-flow communication with said vulcanizing and said cooling chambers, means for withdrawing cooling water from said sump, first baffle means in said sump between said withdrawing means and said vulcanizing chamber, and second baffle means in said sump between said withdrawing means and said cooling chamber, said baffle means acting to prevent the admission of water into the vulcanizing chamber and having openings for the free passage of said cable therethrough without contacting said cable.
 7. An apparatus for continuously curing and cooling an advancing polymeric strand comprising a tube containing a pressurized gas at elevated temperature, means defining a chamber downstream of and communicating with said tube, a sump opening downwardly in said chamber immediately downstream of said tube, refrigerating means, pumping means, piping means connecting said sump to a point in said chamber substantially downstream of said sump through said refrigerating means and said pumping means, said pumping means continuously circulating cooling water from said sump to said downstream point in said chamber, first baffle means in said sump between said piping means and said tube, and second baffle means in said sump between said piping means and said chamber, said baffle means acting to prevent the admission of cooling water into said tube and having openings for the free passage of said strand therethrough without contacting said cable.
 8. The apparatus of claim 7 wherein said tube is formed in a catenary comprising means suspending said strand in a catenary within said tube and said chamber without contact between said strand tube and chamber.
 9. The apparatus of claim 8 wherein said openings are vertically elongated to accommodate the catenary rise of said strand.
 10. The apparatus of claim 11 including a tubular extension projecting substantially horizontally from the lowest point of said catenary, said extension comprising a support for said extrudate suspended in said catenary, the floor of said extension being abruptly elevated above the floor of said catenary tube at said lowest point thereof.
 11. Apparatus for continuously manufacturing an electrical cable having a plurality of concentric coatings comprising first extruder means for receiving and depositing upon an electrically conductive core at least one polymeric coating, a vulcanizing tube connected to said extruder means to receive the coated core, means for maintaining a gas under high heat and pressure in said vulcanizing tube, liquid cooling means connected to said vulcanizing tube for receiving the coated core after passing through the vulcanizing tube, sump means intermediate and in fluid flow communication with said vulcanizing tube and said liquid cooling means, means for withdrawing cooling liquid from said sump, first baffle means between said withdrawing means and said vulcanizing tube, second baffle means between said withdrawing means and said liquid cooling means, said baffle means acting to prevent the admission of cooling liquid into said vulcanizing tube and having openings therethrough for the free passage of said cable therethrough without contacting said cable, jacket extruding means for receiving the coated core directly upon leaving the cooling means and for depositing about the core an extruded jacket, and means for cooling the extruded jacket.
 12. The apparatus in claim 11 wherein said tube and at least upstream portions of said liquid cooling means are formed in a catenary curve matching the natural depending configuration of the core to prevent contact between the coated core, tube and cooling means until the coating is sufficiently hard, the first-mEntioned extruder means comprises means for depositing upon said core a semiconducting shield layer and thereafter an insulation layer, and the jacket extruder deposits drain wire embedded in said jacket.
 13. The apparatus according to claim 11 wherein the tube is filled with an inert noncondensing gas, a jacket surrounds the tube and means are provided for recirculation of hot combustion gases throughout said jacket, the tube is in direct communication with the cooling means comprising cooling water thereby forming a gas-water interface and means are provided for circulating water throughout the cooling means without admission of water into the vulcanizing tube.
 14. The apparatus of claim 7 wherein means are provided for heating the core prior to entering the extruder means. 